Radar Altimeter Location/ Calibration

[troopernflight]

I think I know the answer to this question but I wanted to make sure. The way I understand it, the RA is located in the Center belly region under the fuselage and is calibrated to measure zero based off the height of the landing gear. So, when I hear “10”, that indicates the gear are 10 feet above the ground, not the belly. As I’m judging height on final approach, I wanted to make sure that I should hearing “50” as I cross the threshold and that the gear is actually at 50 feet and not some other point on the aircraft. (I.e.- In a CRJ 900 the gear is significantly lower than my position in the cockpit). Thanks for any insight.

 

[Deleted member 27505]

Depends on what kind of system you're using. Honeywell calibrates to zero at main gear. So accurately that when you're full weight on wheels, it reads negative. I'm far from well informed on the subject, but I suspect all the modern RA/GPWS systems act similarly, especially ones that support autoland. Older ones...?? Check the supplements describing your particular system.